Refillable device with counting means

ABSTRACT

A refillable medical device comprising a base unit ( 4 ) adapted to be engaged with a refill unit ( 2 ), the device comprising means for counting the number of different refill units which are engaged with the base unit ( 4 ). The device may be in the form of a dry powder or pressurised aerosol inhaler, needleless injector, intravenous drip system etc. The device may comprise means to disable the device after a predetermined number of refill units have been used with the base.

FIELD OF THE INVENTION

[0001] This invention relates to refillable devices of the typecomprising a base unit which is engaged with a refill unit and inparticular to refillable medical devices having means to count thenumber of different refill units which have been used with the device.

BACKGROUND TO THE INVENTION

[0002] For reasons of economy and in order to reduce the environmentalimpact of materials usage, there is a growing trend towards the use ofrefillable devices of various kinds rather than the use of disposabledevices. In many cases it is of no great concern how many refill unitshave been used with a particular device. However, other devices may havea limited life span in the interests of device efficiency, consumerprotection, hygiene, manufacturer's liability etc.

[0003] U.S. Pat. No. 5,950,016 discloses a recyclable camera and filmcombination in which the camera comprises means for automaticallyrewinding the film after the last frame in the film has been shot, meansfor controlling the lid so as to automatically open when the entire filmis rewound into the film cartridge, means for counting the number offilm cartridges loaded into the cartridge chamber, and means for makingthe controlling means inoperative, whereby the lid does not open for theremoval of the film cartridge loaded in the cartridge chamber when thecounting means reaches a predetermined number of film cartridges andthus prevent the cartridge chamber from receiving any further filmcartridges.

[0004] U.S. Pat. No. 5,659,837 discloses a developing device in an imageforming apparatus having a cartridge loading portion for loading areplaceable toner cartridge, a frame including a hollow portion forreceiving a developer supplied from the cartridge. A photosensitive druminstalled in the hollow portion and having a surface exposed to theexterior of the frame, and a developer roller installed adjacent to thephotosensitive drum, the developing device having a cartridge controldevice installed on the one side of the cartridge loading portion tocontrol the installation and removal of the toner cartridge in which thecartridge control device includes a cartridge installation and removaldevice for allowing a user to install or remove the toner cartridge, acounter for counting the number of toner cartridge replacements, and acartridge removal protector for prohibiting removal of the tonercartridge from the developing device when a predetermined number oftoner cartridge replacements is reached so as to prevent contaminationresulted from an imbalance between the total amount of the tonersupplied and the capacity of a waste toner container.

[0005] WO92/17231 discloses a medical inhaler featuring amicroelectronic assembly, a receptacle for a container of medication, atriggering element electrically coupled to the microelectronic assembly,positioned inside the receptacle and activated by pressing the containerto release a dose of medication. The microelectronic assembly may be acounter, or an interval timer for recording the dosage history of thecontainer, including time intervals between doses. The inhaler includeselectrical contact fingers contacting an electrical circuit on thecontainer which stores information about the container in digital form.The digital data storage means includes a set of electrically conductivestrips on the container whose spatial pattern represents data about thecontainer and a microelectronic memory. The digital data stored includesthe number of doses remaining, the time interval between dosespreviously actuated, the type of medication, the expiration data, thelot and serial number of the container and other usage information.

[0006] In the medical field there are a range of refillable devices,e.g. for the delivery of medicament, saline etc., to a patient whichwould benefit from a simple, effective system of recording how manyrefill units have been used with a particular device. It would also beadvantageous for the device to be disabled after a predetermined numberof refill units have been used.

BRIEF SUMMARY OF THE INVENTION

[0007] According to the present invention there is provided a refillablemedical device comprising a base unit adapted to be engaged with arefill unit, the device comprising means for counting the number ofdifferent refill units which are engaged with the base unit.

[0008] The invention provides medical apparatus comprising a base unithaving means of counting the number of times fresh refills have beenfitted in the base unit. The apparatus does not repeatedly count thesame refill unit and therefore the same refill unit may be removed andreplaced multiple times e.g. for the purposes of cleaning the base unit,without affecting the count. The base unit may comprise means tovisually indicate to the user the count i.e. the number of fresh refillsthat have been fitted to the base unit. The base unit may comprise meansto disable the base unit or prevent engagement of a fresh refill unitafter a predetermined number of refills have been used with the baseunit. This ensures a base unit is disposed of after its working life orserviced e.g. by replacement of worn components after a predeterminedamount of use.

[0009] The invention finds particular utility in the medical field inapparatus for delivery of medicament to a patient e.g. dry powderinhalers, pressurised aerosol inhalers, needleless injectors,intravenous line apparatus etc.

[0010] The means for counting the number of different refills are ofsimple mechanical construction which do not require the presence ofbatteries, motors, microprocessors etc. The counting means need not addsignificantly to the cost of the device while providing a simple andreliable means of counting the number of refill units used andoptionally disabling the device.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0011] The means for counting the number of different refills may take avariety of different forms.

[0012] According to one embodiment each refill unit comprises a tabwhich is engaged by the base unit when the refill is fitted thereto.Upon removal of the refill the tab is broken off the refill unit andremains within the base unit as an indication a refill unit has beenfitted to the base unit. Thereafter the original refill unit may beengaged and disengaged from the base unit without increasing the“count”. When a new (second) refill unit complete with tab is fitted tothe base unit the second tab is engaged by the base unit and is retainedby the base unit when the second refill unit is removed thus providingan indication that a second refill unit has been used. The base unit maybe constructed to prevent engagement of a new refill with tab after apredetermined number of refills have been used with the base unit. Forexample, the storage space of the base unit for the tabs may havedimensions to accommodate a specific number, say 5, tabs and thereafterengagement of a further tab is prevented since access is prevented bythe tabs filling the space.

[0013] According to a second embodiment the base unit comprises acounting device comprising a display which may be incrementally moved todisplay a count e.g. a rotatable wheel, ring or disc. The refill unitcomprises an actuator e.g. a projecting finger, which causes incrementalmovement of the counting device when the refill unit is initiallyengaged with the base unit and upon first engagement or first removal ispermanently deformed or snapped off such that removal and subsequentreplacement of the refill unit will not cause further movement of thecounting device.

[0014] In accordance with one embodiment the device is in the form of apressurised aerosol inhaler and the refill unit comprises a pressurisedaerosol container.

[0015] In accordance with a further embodiment the device is in the formof a needleless injector and the refill unit comprises a container ofmedicament to be injected which may be in liquid or powder form.

[0016] In accordance with further embodiments the device is in the formof an intravenous drip system and the refill unit comprises a bag orcontainer of saline, blood etc.

BRIEF DESCRIPTION OF DRAWINGS

[0017] The invention will be described with reference to theaccompanying drawings in which:

[0018]FIG. 1 represents an exploded cross-sectional view through adry-powder inhaler comprising a base unit and a refill unit,

[0019]FIG. 2 represents a cross-sectional view of the assembleddry-powder inhaler of FIG. 1,

[0020]FIG. 3 represents a cross-sectional view of the base unit of theinhaler of FIGS. 1 and 2 with a tab from the refill unit of FIG. 1 init,

[0021]FIG. 4 represents a cross-sectional view of the base unit of theinhaler of FIGS. 1 and 2,

[0022]FIG. 5 represents a cross-sectional view of an alternative baseunit of a dry-powder inhaler,

[0023]FIG. 6 represents a fragmentary cross-section through analternative form of tab to that shown in the refill unit in FIGS. 1 and2,

[0024]FIG. 7 represents a cross-section through a tab suitable for useon a refill unit for use in the invention,

[0025]FIG. 8 represents a cross-section through a base unit containingtabs as shown in FIG. 7,

[0026]FIG. 9 represents an exploded view of a pressured aerosol inhalercomprising a base unit and a refill unit,

[0027] FIGS. 10 to 12 represent views of the inside of the inhaler ofFIG. 9 at different stages during the insertion and removal of therefill unit.

[0028]FIG. 13 represents an exploded view of a pressurised aerosolinhaler comprising a base unit and refill unit,

[0029]FIG. 14 represents a first fragmentary section through the inhalerof FIG. 13 showing the arrangement of the tab,

[0030]FIG. 15 represents a second fragmentary section through theinhaler of FIG. 13,

[0031]FIG. 16 represents an exploded view of a further inhaler inaccordance with the invention,

[0032]FIG. 17 is a schematic diagram of an intra-venous drip system inaccordance with the invention and

[0033]FIG. 18 is a schematic diagram of part of a needleless injector inaccordance with the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0034]FIG. 1 shows a replaceable refill unit (2) capable of reversibleinsertion into a base unit in the form of a reusable inhaler device body(4). The refill unit (2) is in the form of a cassette comprising aflanged spool (8) loaded with medicament-bearing tape (10). Such tapesare disclosed in U.S. Pat. No. 5,192,548. The inhaler body incorporatesbreath actuated means (not shown) to release the micronised medicamentpowder from the tape. For example, a triggering release mechanism (notshown) is housed in region (6) of the inhaler device body (4). Fulldetails of such inhalers are disclosed in WO90/13327, WO90/13328 andWO92/08509.

[0035] The refill unit (2) and device body (4) shown in FIG. 1incorporate features of the present invention. The cassette (2) includesa tab portion (12) comprising a plurality of barbed flexible legs (16)and integrally joined to the cassette only by thin finger elements (14).(For convenience, in FIG. 1, the tab (12) is shown moulded as anintegral part of the spool (8), although it may be moulded as part ofsome non-rotating cassette component.) The device body (4) comprises ameans for counting (18) in the form of a cylindrical storage chamber(20) having a frustoconical inlet (19) which has a diameter slightlysmaller than that of the chamber (20) to create an annular retainingledge (21).

[0036] In use the patient inserts a replaceable cassette (2) into theinhaler device body (4), causing the detachable tab (12) to enter thestorage chamber (20), with its flexible legs (16) biased inwards by theinlet (19), and then released to spring outwards once the inhaler hasbeen assembled (FIG. 2).

[0037] For each subsequent new cassette refill inserted, a furtherdetachable tab (12 a, 12 b, 12 c, etc.) will be deposited into thechamber (20) in the device body (4). FIG. 4 shows the device body afterfour fresh refills have been inserted and removed in turn. At thispoint, the patient is warned not to use the device body further by theappearance of a tab (12) near opening (22). This prevents the patientfrom tending to use the reusable device body with more refills than itsintended life. This is important for pharmaceutical devices, such asinhalers, where over-use of an inhaler might result in enough wear andtear to prevent it dispensing accurate and safe doses.

[0038] In one embodiment (not shown) a transparent window is securedover opening (22), preventing insertion of further refills afterinsertion of the intended number of refills. Generally in pharmaceuticaldevices, however, it is desirable to allow the continued refilling ofthe device body, in order to provide contingency for emergencies whenthe patient has not appreciated they have reached the intended refillnumber limit. In this case, any additional cassettes inserted willresult in earlier tabs being expelled from the device through theopening (22). The visible (and possibly tactile, for vision impairedpatients) presence of a tab near the opening (22) will continue toremind the patient to obtain a new device body (4), however.

[0039] An additional feature of the invention is that provision could bemade to store X+1 tabs in the storage space (20), where X is theintended maximum number of refill units. In this case, the patient wouldbe able to see the tabs accumulating in the storage space (20), and awarning line would show them when X cassettes had been inserted. Onepurpose of the X+1th space would be to give the manufacturer warningthat the device body (4) had been used beyond its guaranteed life, forproduct liability reasons.

[0040] It will be appreciated that the detachable tabs (12) are wellprotected from tampering inside the cassette (2). As an additionalsecurity feature, for example to prevent malicious product liabilitydisputes or claims, the internal surfaces of the chamber (20) could bemoulded smooth to allow microscope examination for scratches caused bytabs that have entered the chamber (20) but have subsequently beenpushed out through opening (22) by a tampering patient.

[0041]FIG. 5 shows schematically a device body (4) comprising a meansfor counting comprising a storage chamber (20) for tabs. This chamber(20) is in the form of a quadrant arc and a straight portion and servesthe purpose of holding a considerably greater number of detachable tabsthan the embodiment shown in is FIGS. 1 to 4. Alternatively, the tubecould be in the form of a semi-circular arc (not shown) to cause thetabs to reach the top surface (24) of the device body when the devicehas reached its design life, thus providing a more forceable reminder tothe patient that a new device body should be obtained.

[0042]FIG. 6 shows schematically (at higher scale) an alternativedetachable tab portion (12) suitable for use in the present invention,comprising an open cup with sloping walls (28) of sufficient flexibilityto act in a manner analogous to that of the flexible legs (16) inFIG. 1. The rim (26) of said walls, which may not be continuous around3600, is arranged to interface with the circular retaining ledge (21),to prevent the tab (12) being removed from the storage chamber (20) uponrefill removal, but instead to cause the thin finger portions (14)attached to the refill (2) to tear. The advantage of such a tab geometryis that the tabs can stack much closer together, inside one another,allowing more tabs to be stored in a given device body thickness.

[0043] An alternative embodiment of the invention is shown schematicallyin FIGS. 7 and 8. This embodiment is also suitable for storing a largenumber of tabs in a small device body thickness. The tabs (12) are inthe form of wedges, having angled surfaces (32, 34) and a notch (36). Athin integral flexible finger (14) attaches the tab (12) to the refillcassette (not shown).

[0044] The device body (4) (shown in part) comprises a tab storagechamber (20) with a straight portion (30) in which many tabs can beheld. The angled surfaces (32, 34) serve to allow each subsequent tab topush its predecessors sideways along the straight portion of tube (30).The hinged top (38) of each tab is pushed down slightly by the tuberoof, causing the notch (36) to close-up slightly and thereby allowingthe tabs to be held in place in the tube. Alternatively, smallprojections (not shown) at the tube opening (22) could be provided toprevent tabs being shaken out of the device body, whilst allowing themto be pushed out by further tabs in an emergency.

[0045] As an alternative (not shown), the opening (22) of FIG. 8 mightbe closed off, and the tabs not provided with hinged tops (38), in orderthat there is no possibility of stress relaxation causing the hingedtops to loosen in the tube (30).

[0046] The tabs (12) could be coded to enable the manufacturer, user,patient or doctor etc., to know what variants or batch numbers of refillunits had been used in a device body.

[0047] FIGS. 9 to 12 illustrate the application of the present inventionto a breath actuated pressurised aerosol inhaler. Full details of theinhaler are not shown but are disclosed, for example in GB2263873 thedisclosure of which is incorporated herein by reference. Examples ofsuch inhalers are commercially available under the registered trade markEASI-BREATHE from Baker Norton.

[0048] The inhaler comprises a base unit which comprises a housingincorporating a mouthpiece and breath actuation mechanism. Part of thehousing is shown at (40). A refill unit is in the form of a pressurisedaerosol container (42) having secured thereto in the region of the valveferrule a ring component 44 having a downwardly projecting finger 46.

[0049] The base unit (40) is provided with a counter 48 in the form of arotating disc. The disc may be viewed through a window (not shown) inthe back of the inhaler housing and the disc contains appropriatemarking to signify the number of counts. The back of the disc comprisesa toothed wheel (50).

[0050] When the refill unit is inserted in the base unit the downwardlyprojecting finger (46) engages a tooth on the toothed wheel (50) causingthe wheel and disc to rotate by one increment (FIG. 10). As insertion ofthe refill unit is completed the finger (46) engages the curved surface(52) in the base unit causing the finger (46) to be permanently deformed(FIG. 11). This deformation is aided by a notch (54) part way along thefinger (46). Thereafter the refill unit may be repeatedly removed andinserted in the base unit without incrementing the counter since thedeformed finger is no longer able to engage the toothed wheel. In analternative embodiment (not shown), insertion or removal of the refillunit might cause the finger to break off.

[0051] The counter can be designed to allow a set number of aerosolrefills to be used by varying the number of teeth. After the set numberof aerosol refills have been inserted it may either show a visualwarning that a new device is now required, possibly through a window inthe device, or it may have a mechanism that would prevent any furtheraerosol refills being added, or both.

[0052] The ring component (44) attached to the ferrule may have alocating feature to ensure the finger will always line up with thecounter. It may also be covered with a shrouding component to protectthe finger before the aerosol refill is fitted to the device. Aninterlocking system may be incorporated to prevent the shroudingcomponent from exposing the finger unless it is fitted into the inhaler.

[0053] FIGS. 13 to 15 illustrate the application of the invention to adifferent breath actuated pressurised aerosol inhaler. Full details ofthe inhaler are disclosed in EP 147028 the disclosure of which isincorporated herein by reference. Examples of such inhalers arecommercially available under the registered trade mark AUTOHALER from 3MUnited Kingdom plc.

[0054] The inhaler includes a base unit comprising a housing (60)defining a mouthpiece and a nozzle block and triggering mechanism (62).The refill unit comprises aerosol container (64) and upper and lowerring components (66, 68). The upper ring component (66) is secured tothe aerosol container (64) and comprises a finger (70). The lower ringcomponent (68) comprises a tab (72) held by thin web elements (74).

[0055] The lower ring component (68) is held captive to the upper ringcomponent (66) with a number of barbed features (67) which prevent thetwo components from coming apart but will allow them to come closertogether when the refill unit is fitted to the base unit. When therefill unit is fitted to the base unit, and the aerosol is actuated inthe device for the first time, the upper and lower components cometogether causing the finger (70) on the upper component to break the tab(72) off the lower ring component and push it into a channel (76) formedon the back of the nozzle block of the base unit. The tab (72) isprevented from falling out of the channel (76) by a slight interferencefit. Following insertion of the refill unit and the breaking of the tab,the aerosol and upper component will be free to move up and down duringnormal actuation of the device. The refill unit may be removed andreplaced.

[0056] New refill units can be inserted into the base unit and tabsbroken off until the channel (76) is full, actuation of subsequentfurther refill units being prevented by the presence of the final,additional captive tab.

[0057] Additional features may be incorporated to prevent the upper andlower ring components coming together until they are assembled in thebase unit, thus preventing the tab (72) from being prematurely brokenoff and not captured in the channel of the base unit which would defeatthe function of the system of the invention. FIGS. 15(a) and (b)illustrate such an arrangement. Upper ring component comprises a pin(80) which is partially accommodated in a recess (81) in the lower ringcomponent (68) prior to assembly with the base unit. The pin (80) isprevented from fully entering the recess (81) by engagement with ledge(83) (FIG. 15(a)). The nozzle block (62) of the base unit comprises aguide finger (82) and when the upper and lower ring components areengaged with the base unit the guide finger (82) deflects pin (80) awayfrom ledge (83) allowing pin (80) to fully enter recess (81). Tab (72)is broken off as the upper and lower ring components come fully togetheras they are assembled with the base unit (FIG. 15(b)).

[0058] In an alternative embodiment the base unit could start with asupply of tabs, which would then be removed, one by one, by insertion ofrefill units. A refill unit is configured so that it could not be usedsuccessfully unless a tab is present: for example, the tab from the baseunit might be necessary to hold the refill in place, or to allow it tooperate (e.g. mechanically). The individual refill units are onlycapable of a single insertion. The base unit is limited in its number ofreuses. It is necessary to ensure that old tabs could not be used to“resupply” the base unit for unauthorised further use.

[0059]FIG. 16 shows an example of such an embodiment which comprises abase unit (200) with a supply of six integrally moulded plastic tabs(202 a etc.) and with a recess (204) for aligning a refill unit inplace. A refill unit (206) for use with this base unit has acorresponding raised area (208) to align with recess (204). An aperture(210) in the refill unit, with an overhanging lip edge (not shown)serves to align with one of the tabs (202 a).

[0060] In use, the user fits the refill unit (206) into the base unit(200), in such a way that the raised area (208) aligns with the recess(204) and one of the tabs (202 a) aligns with the hole (210). The tab(202 a) serves to locate and secure the refill unit (206) in the baseunit (200) in such a way that it can be successfully used. When therefill unit (206) is subsequently removed, the lip (not shown) of thehole (210) causes the captive tab (202 a) to fracture from the base unit(200) at its proximal end. That tab (202 a) thus remains in the refillunit (206) and is protected from easy removal by the user, thuspreventing re-use of the spent refill unit (206). The unit (200)meanwhile has “counted” one refill unit and now only has five remainingtabs (202 b etc.) for further use. The user must then align the baseunit (200) with the next refill unit such that the latter's hole alignswith one of the five remaining tabs (202 b etc.).

[0061] In an alternative embodiment (not shown), the base unit comprisesa spring loaded supply of stacked tabs to advance tabs sequentially. Therefill unit is configured to engage with (and subsequently remove) theoutermost tab of the stack only.

[0062]FIG. 17 shows schematically a replaceable refill unit (302)comprising a flexible bag (350) containing blood, saline etc. andcapable of reversible insertion into a base unit (304) in the form of aconnector plate (352) fitted to a tubing line (354) connected to anintravenous needle (356) inserted in a patient's arm (not shown).Similar systems, but without the counting means of the presentinvention, are disclosed in U.S. Pat. No. 5,947,937 the disclosure ofwhich is incorporated herein by reference. For example the refill unitmay have configurations and fittings (358, 362) which provide coding forthe blood group in the flexible bag (350). The connector plate (352)would have a geometry and/or fittings of a shape coding for therecipient patient's blood group, such that only refill units (302)containing the same blood group would be capable of insertion into theconnector plate (352).

[0063] The refill unit (302) and base unit (304) shown in FIG. 17incorporate features of the present invention. The refill unit includesa tab portion (312) of similar form and mounting as tab portion 12 ofFIG. 1. The base unit (304) comprises a cylindrical storage chamber(320) having an inlet geometry of the type possessed by the storagechamber (20) of FIG. 1.

[0064] In use, a blood containing replaceable refill unit (302) isinserted into the base unit (304), causing the end (364) of the tubingline (354) to mate with the inside bore (360) of the refill unit'sconnector fittings (362), thereby allowing blood from the flexible bag(350) to pass via the tubing (354) and the hypodermic needle (356) intothe patient's arm (not shown). Insertion of the refill unit (302) intothe base unit (304) also causes the detachable tab (312) to enter thestorage chamber (320) and to be left there upon removal of the refillunit (302). In this way, a record is left in the base unit (304)connected to the patient of how many refill units of blood have beensupplied to the patient. It is clearly of importance to know thisinformation, and this invention provides automatic means of recordingthe number of blood bags supplied.

[0065]FIG. 18 shows schematically a replaceable refill unit (402)comprising a medicament vial (450) containing a liquid medicamentformulation (448) to be administered to the skin. The replaceable refillunit (402) also comprises a plastic connector (480) capable ofreversible engagement with a needleless jet injector system (shownpartially at 490) in the form of a base unit (404). When the vial (450)and connector (480) are assembled together, a narrow exit passagewayfrom the vial (450) is formed via a vial-piercing needle (470) and aninternal tube (472), The injector system (490) comprises a spring-drivenpiston (478) in a cylinder (476), use of which piston arrangement, afterthe refill unit (402) has been disengaged, allows administration of adose of medicament in the form of a high velocity liquid jet from thecylinder (476) via the nozzle (474) into the patient's skin (not shown).

[0066] Similar refill systems for needleless jet injector systems, butwithout the counting means of the present invention, are disclosed inU.S. Pat. No. 4,507,113 and 4,883,483 the disclosure of which isincorporated herein by reference.

[0067] The refill unit (402) and base unit (404) shown in FIG. 18incorporate features of the present invention. The refill unit includesa tab portion (412) of similar form and mounting as tab portion 12 inFIG. 8. The base unit (404) comprises a storage chamber (420) of asimilar type to that shown in FIG. 8.

[0068] In use, a replaceable refill unit (402) is engaged with theneedleless jet injector base unit (404), thereby allowing medicamentformulation from the vial (450) of the refill unit (402) to be drawninto the cylinder (476) of the jet injector (490). Insertion of therefill unit (402) into the base unit (404) also causes the detachabletab (412) to enter the storage chamber (420) and to be left there uponremoval of the refill unit (402). In this way, a record is left in theneedleless injector's base unit (404) of how many refill units have beenused with the jet injector (490). This information may be important forproviding a record of the medicament administered to an individualpatient, and may also be of importance for monitoring use of aparticular jet injector where uncontrolled re-use before disposal isundesirable.

[0069] It will be appreciated that other arrangements of the presentinvention, including ones compatible with a bayonet or screw engagementaction, are possible. It will also be apparent that the presentinvention is also suited to other applications, such as use inrefillable dry powder needleless injection systems such as thatdisclosed in U.S. Pat. No. 5,899,880 the disclosure of which isincorporated herein by reference.

1. A refillable medical device assembly comprising a refill unit and a base unit adapted to engage the refill unit, said base unit comprising means for counting the number of different refill units which have been engaged with the base unit.
 2. A refillable medical device assembly as claimed in claim 1 in which the means for counting does not repeatedly count the same refill unit.
 3. A refillable medical device assembly as claimed in claim 1 or claim 2 in which the base unit comprises means to visually indicate to the user the number of different refill units that have been engaged with the based unit.
 4. A refillable medical device assembly as claimed in any preceding claim in which the means for counting comprises a chamber adapted to receive a tab attached to the refill unit and means to engage and detach said tab from the refill unit.
 5. A refillable medical device assembly as claimed in claim 4 in which the chamber is dimensioned to accommodate a predetermined number of tabs whereupon engagement of a fresh refill unit with the base unit is prevented.
 6. A refillable medical device assembly as claimed in claim 5 in which the base unit is constructed so that tabs present in the chamber are visible.
 7. A refillable medical device assembly as claimed in claim 3 in which said visually indicating means comprises a display, the display being capable of incremental moved upon engagement of a new refill unit.
 8. A refillable medical device assembly as claimed in claim 7 in which the display is in the form of a rotatable disc.
 9. A refillable medical device assembly as claimed in claim 8 in which the rotatable disc is associated with a toothed wheel which is engaged by a finger attached to the refill unit to incremental move the disc, the base unit additionally comprising means to deform or break said finger to prevent subsequent engagement of the finger with the toothed wheel.
 10. A refillable medical device assembly as claimed in claim 1 in which the means for counting comprises a chamber in the refill unit adapted to receive a tab attached to the base unit and means to engage and detach said tab from the base unit when the refill unit is detached from the base unit.
 11. A refillable medical device assembly as claimed in any preceding claim in which the device is a dry powder inhaler and the refill unit is in the form of a cassette having a tape bearing powdered medicament.
 12. A refillable medical device assembly as claimed in any one of claims 1 to 9 in which the device is a pressurised aerosol inhaler and the refill unit comprises a pressurised aerosol container.
 13. A refillable medical device assembly as claimed in claim 10 or claim 11 in which the inhaler is breath actuated.
 14. A refillable medical device assembly as claimed in any one of claims 1 to 9 in thc form of a needleless injector.
 15. A refillable medical device assembly as claimed in any one of claims 1 to 9 in the form of an intravenous drip system. 